Extractive oxidation used as a naphtha treating process is well-known, for example, the sweetening naphtha process, typically comprising a catalytic oxidation via O2 in the presence of NaOH or KOH of odor-generating mercaptans of certain raw naphthas, more specifically those from fluid catalytic cracking. See U.S. Pat. No. 2,591,946 where is taught a sweetening process for sour oils whereby mercaptans are removed from said oils by carrying out a reaction the catalyst of which is KOH, O2 and 0.004 to 0.1 wt % copper oxide based on the KOH solution.
Also, an article in the Oil and Gas Journal vol. 57 (44) p. 73–78 (1959) entitled “Low Cost Way to Treat High-Mercaptan Gasoline” by K. M. Brown et al, is directed to the discussion of the Merox process and other prior art procedures.
Also, an oxidizing/extracting process is reported in U.S. Pat. No. 6,406,616, said process being exclusively focused on the removal of up to 500–600 ppm sulfur from gasoline streams as exemplified therein, the oxidation reaction being performed by a mixture of peroxide and formic acid. One alternative presented is a self-extractive oxidation process and another one includes a further adsorption step over an alumina bed.
However, such state-of-the-art processes do not apply to highly contaminated raw naphthas such as those having sulfur contents of 8000 ppm or more, nitrogen contents of 2000 ppm or more, including other unstable compounds, which cause rapid self-degradation of the stream. More specifically such state-of-the-art processes are exclusively applied to remove or to sweeten sulfur-containing compounds. Particularly, said processes are not suitable to removing or stabilizing non-sulfur compounds, for instance substances containing nitrogen functionalities. Among those, should be mentioned mainly those nitrogen functionalities of a basic character, which cause not only odor but also naphtha instabilities due to color as well as turbidity. Besides, those basic nitrogen substances are harmful to the hydrodesulfurization treatment processes used as naphtha finishing processes before commercialization.
The peroxide-aided oxidation is a promising path for the refining of fossil oils, and may be directed to several goals, for example to the removal of sulfur and nitrogen compounds present in fossil hydrocarbon streams, mainly those used as fuels for which the international specification as for the sulfur content becomes more and more stringent.
One further application is the withdrawal of said compounds from streams used in processes such as hydrotreatment, where the catalyst may be deactivated by the high contents in nitrogen compounds.
Basically, the peroxide oxidation converts the sulfur and nitrogen impurities into higher polarity compounds, those having a higher affinity for polar solvents relatively immiscible with the hydrocarbons contaminated by the sulfur and nitrogen compounds. This way, the treatment itself comprises an oxidation reaction step followed by a separation step of the oxidized products by polar solvent extraction and/or adsorption and/or distillation.
The oxidation reaction step using peroxides, as well as the separation steps of the oxidized compounds from the hydrocarbons have been the object of various researches.
Thus, EP 0565324A1 teaches a technique exclusively focused on the withdrawal of organic sulfur from petroleum, shale oil or coal having an oxidation reaction step with an oxidizing agent like H2O2 initially at 30° C. and then heated at 50° C. in the presence of an organic acid (for example HCOOH or AcOH) dispensing with catalysts, followed by (a) a solvent extraction step, such as N,N′-dimethylformamide, dimethylsulfoxide, N,N′-dimethylacetamide, N-methylpyrrolidone, acetonitrile, trialkylphosphates, methyl alcohol, nitromethane among others; or by (b) an adsorption step with alumina or silica gel, or (c) a distillation step where the improved separation yields are caused by the increase in boiling point of the sulfur oxidized compounds.
A similar treatment concept is used by D. Chapados et al in “Desulfurization by Selective Oxidation and Extraction of Sulfur-Containing Compounds to Economically Achieve Ultra-Low Proposed Diesel Fuel Sulfur Requirements”, NPRA 2000 Annual Meeting, Mar. 26–28, 2000, San Antonio, Tex., Paper AM-00-25 directed to a refining process also focused on the reduction of the sulfur content in oils, the oxidation step occurring at temperatures below 100° C. and atmospheric pressures, followed by a polar solvent extraction step and by an adsorption step. The authors further suggest the use of a solvent recovery unit and another one for the biological treatment of the concentrate (extracted oxidized products) from the solvent recovery unit, this unit converting said extracted oxidized products into hydrocarbons.
According to the cited reference by Chapados et al., the reaction phase consists of an oxidation where a polarized —O—OH moiety of a peracid intermediate formed from the reaction of hydrogen peroxide and an organic acid performs an electrophilic oxidation of the sulfur compounds, basically sulfides such as benzothiophenes and dibenzothiophenes and their alkyl-related compounds so as to produce sulfoxides and sulfones.
U.S. Pat. No. 3,847,800 teaches that the oxidation of nitrogen compounds, such as the quinolines and their alkyl-related compounds so as to produce N-oxides (or nitrones) can be promoted as well when reacting these compounds with a nitrogen oxide.
The mechanisms for the oxidation of sulfur containing compounds with a peracid derived from a peroxide/organic acid couple are shown in FIG. 1 attached, with dibenzothiophene taken as model compound.
According to U.S. Pat. No. 2,804,473, the oxidation of amines with an organic peracid leads to N-oxides, therefore a reaction pathway analogous to that of sulfur-containing compound is expected for the oxidation of nitrogen-containing compounds with a peracid derived from the peroxide/organic acid couple, as shown in FIG. 2 attached, with quinoline taken as model compound. In addition, the same US patent teaches a process for the production of lower aliphatic peracids. According to this publication, peracids are useful in a variety of reactions, such as oxidation of unsaturated compounds to the corresponding alkylene oxide derivatives or epoxy compounds.
As illustrated in FIG. 3 attached, it is also well-known that hydrogen peroxide naturally decomposes into unstable intermediates that yield O2 and H2O, such process being accelerated by the action of light, heat and mainly by the pH of the medium.
U.S. Pat. No. 5,310,479 teaches a process for desulfurizing crude oil by means of an aqueous oxidant solution made up of formic acid and hydrogen peroxide. The oxidant is supposed to oxidize the aliphatic sulfur content of the crude oil. After the reaction the oil is washed with water to separate the oxidized products. The proposed technique is limited to aliphatic sulfur. In view of the incompatibility of water and crude oil, it is expected that much foam will be formed upon admixing of the aqueous oxidant solution and the crude oil. No mention is made to the removal of any nitrogen compound.
U.S. Pat. No. 6,406,616, already mentioned above, teaches a process for desulfurizing hydrocarbons such as gasoline and similar petroleum products to reduce the sulfur content to a range of from about 2 to 15 ppm sulfur without affecting the octane rating. The sulfur-containing hydrocarbon is contacted at slightly elevated temperatures with an oxidizing/extracting solution of formic acid, a small amount of hydrogen peroxide, and no more than about 25-wt % water. However, said U.S. patent is limited to fuel containing up to 500 ppm sulfur, that is why low (2–3%) H2O2 concentrations are used. FIG. 2 of this patent illustrates an alternative whereby an alumina adsorption step is proposed. Adsorption is directed to fulfill the removal of sulfur compounds, mainly oxidized thiophene compounds. Qualitative results ensuing sulfur removal after adsorption are not mentioned. In spite of stating that oxidized products contain of from 2 to 15 ppm sulfur, examples do not mention real figures for sulfur. Also, in spite of the fact that it is stated that the octane rating of the fuel is not affected by the oxidation, no octane rating measurement is provided. Also, said U.S. patent does not mention the reduction of non-sulfur substances contents, such as the nitrogen-containing compounds or others that may promote a troublesome unstable behavior and less-acceptable aspect of the hydrocarbon stream when used as feedstock of other refining process or as a final treated product.
Published U.S. Application No. 20020189975 of the Applicant and fully incorporated herein as reference, teaches the catalytic oxidation of organic compounds in a hydrophobic, fossil oil medium in the presence of a peracid (or peroxide/acid couple). The oxidation reaction is catalyzed by an iron oxide such as a pulverized limonite ore working as a highly dispersible source of catalytically active iron in this oil medium.
U.S. Ser. No. 10/314,963 of Dec. 09, 2002 of the Applicant and fully incorporated herein as reference, teaches the application of the peroxide/acid couple catalyzed by an iron oxide to a raw naphtha. The process is directed to the simultaneous oxidation and removal and/or inertization of the sulfur, nitrogen, conjugated dienes and other unsaturated compounds from said naphtha streams in the presence of said iron oxide catalyst.
Thus, the literature mentions processes for the treatment of a sulfur-containing fuel through oxidation in the presence of peracids (or peroxides and organic acids), or as in published application U.S. 20020189975A1, processes directed to the catalytic oxidation of organic compounds in a hydrophobic, fossil oil medium in the presence of a peracid (or peroxide/acid couple), the oxidation reaction being catalyzed by an iron oxide such as a pulverized limonite ore working as a highly dispersible source of catalytically active iron in this oil medium. However, there is no description nor suggestion in the literature of an auto-extractive oxidation of any heteroatomic polar compounds from raw hydrocarbon streams to remove specially high contents of nitrogen compounds while simultaneously removing and/or inertizating sulfur compounds to some extent aiming specially at minimizing strong harmful odor and color instability, whereby such compounds are oxidized in the presence of an aqueous peroxide solution/organic acid couple, the weight percent of the peroxide solution and organic acid based on raw naphtha being at least 3 for both peroxide solution and organic acid, said compounds being simultaneously removed from said streams by the oxidant itself, said process being described and claimed in the present invention.